1. Field of the Invention
The subject disclosure relates to guided weapon systems, and more particularly to an improved guidance system employing an imager and a method for designating a target which provides precision strike capability but that does not need the active-designate-until-impact requirement.
2. Background of the Related Art
Typical weapon guidance systems utilize target designation systems to achieve high accuracy hit-placement. In existing technology, a semi active laser (SAL) target designator (LTD) is used to illuminate an intended target or a chosen spot on a target. The weapon system homes in on illumination reflected from the target to strike the target. These laser guided weapons require the laser designator operator (LDO) to designate the target until weapon impact. Hence, the laser designator operator must remain in the target vicinity. By being in the target vicinity, the LDO such as a forward observer or designator aircraft and the associated crew, are in danger. Such targeting systems are considered active. Examples of targeting systems are disclosed in U.S. Pat. No. 3,321,761 issued on May 23, 1967 to Biagi et al. and U.S. Pat. No. 3,652,837 issued on Mar. 28, 1972 to Perkins, U.S. Patent App. Pub. No. 2011/0017864 A1 published on Jan. 27, 2011 to Roemerman, U.S. Pat. No. 4,347,996 issued Sep. 7, 1982 to Grosso, and U.S. Pat. No. 7,059,560 B2 issued Jun. 13, 2006 to Ljungberg et al.
Active laser guided weapons which are designate-until-impact impose limitations on operations. First, a line of sight (LOS) must exist between the designator and target and between the target and laser acquisition system on the weapon. Second, the direction of attack must allow the laser acquisition system to sense sufficient energy reflected from the designated target, minimize false target indications, and preclude the weapon from guiding onto the designator. Finally, the laser designator must designate the target at the specific correct time and for the proper duration.
Various guided weapons also have viewing systems to capture and evaluate images containing the target and its surrounding region as seen from the weapon. This allows the weapon to track targets passively. However, passive image guided weapons require a means to detect and acquire a target autonomously. Autonomous target acquisition requires preloaded images or models of the desired target and a means of correlating or matching the preloaded images with the live current image as seen from the weapon during flight. These methods are limited in operation due to the large number of possible closure geometries and environmental conditions required in the preloaded target images. For examples, see U.S. Pat. No. 5,201,895 issued Apr. 13, 1993 to Grosso, U.S. Pat. No. 4,690,351 issued Sep. 1, 1987 to Beckerleg et al., U.S. Pat. No. 5,052,045 issued Sep. 24, 1991 to Peregrim et al., U.S. Pat. No. 5,881,969 issued on Mar. 16, 1991 to Miller, U.S. Pat. No. 5,890,808 issued on Apr. 6, 1999 to Neff et al., and U.S. Pat. No. 6,157,875 issued on Dec. 5, 2000 to Hedman et al., as well as U.S. Pat. No. 6,529,614 B1 issued on Mar. 4, 2003 to Chao et al.
Such systems require an on-board high-resolution, variable magnification lens system, which greatly increases the cost and complexity of the weapon. Further, such systems do not have a direct assessment at launch time of the weapon's ability to acquire or maintain lock using the preloaded images. Lacking this assessment to compute a probability of success metric leads to weapon launches that fail to acquire a lock and thus never strike the intended target. Such a failure requires a post mission analysis to determine why the weapon failed and reduces the confidence in the system. Missing a real time predictive success metric also prevents the weapons launch officer from modifying the parameters of the mission which would otherwise improve the odds of success.
Various guided weapons also combine active laser designation and passive imaging so that the benefits of both can be used. Typically active designation is used to acquire the target and passive imaging is used to track the acquired target to impact. Examples of these mixed-mode systems are U.S. Pat. No. 6,987,256 B2 issued on Jan. 17, 2006 to English et al., U.S. Pat. No. 6,111,241 issued on Aug. 29, 2000 to English et al., and U.S. Pat. No. 7,858,939 B2 issued on Dec. 28, 2010 to Tener et al. However, these kinds of combined systems are also very costly and complex, particularly considering that the entire weapon is intended to be expendable. In order for successful operation, there is the need to ensure the proper hand-off between the laser designation of the target and the passive acquisition of said target. One such method of aligning these two subsystems is given in U.S. Pat. No. 7,909,253 issued on Mar. 22, 2011 to Sherman.
In order to reduce image guided weapon total cost, some weapons attempt to eliminate portions of the navigation system required to deliver the weapon into the vacinity of the target. By providing a pre-loaded database of geo-referenced images, an on-board imager attempts to correlate the current view from the weapon with the database images to estimate current location, velocity, acceleration and other navigation information. For examples of such image-aided navigation systems, see U.S. Pat. No. 7,725,257 issued on May 25, 2010 to Strelow et al., U.S. Pat. No. 7,191,056 issued on Mar. 13, 2007 to Costello et al., and U.S. Patent App, Pub. No. 2009/0248304 A1 published on Oct. 1, 2009 to Roumeliotis et al. However, these systems require that the images in the database be accurately geo-referenced, which is a costly process.